Apparatus for measuring the flow velocity of fluids

ABSTRACT

The apparatus comprises two ultrasonic transducers spaced apart and arranged in the line of flow to be measured. The transducers are connected to act as both transmitters and receivers. The time of travel of a pulse of ultrasound in the direction of flow is compared with the time of travel of a pulse of ultrasound in the reverse direction. The fluid paths traversed are thus identical, but the pulses are slightly separated in time.

O United States Patent 1151 3,678,73 1 Wells etal. 1 July 25, 1972 [54]APPARATUS FOR MEASURING THE 2,708,366 5/1955 BIOChCI et al .73/194 A xFLOW VELOCITY ()F'FLUIDS 3,171,095 2/ 1965 Gennari ..73/194 A X2,911,825 11/1959 Kritz... ..73/l94 A [72] Inventors: Frank HerbertWells, Abmgdon, England; 2993373 7/1961 Kmz I "73/194 A Nwma" late of3,204,456 9/1965 Welkowitz ..73/194 A Newbury, P$ Cathefme Margat3,237,453 3/1966 Yamamoto et al... ..73/194 A Daveyfidmmlstra 3,473,37810/1969 Yoshiyama Clfll ..73/194A [73] Ass1gnee:ggrggnmlsggrilidifitomic Energy Authority, FOREIGN PATENTS ORAPPLICATIONS [22] Filed Sq) 29 1967 146,517 8/1962 U.S.S.R ..73/l94A[21] Appl. No.: 870,377 Primary lzltuminer-Charles A. Ruehl A/mrnev-Larson, Taylor & Hinds [30] Foreign Application Priority Data 57 IABSTRACT 1968 Great Bmam The apparatus comprises two ultrasonictransducers spaced apart and arranged in the line of flow to bemeasured. The E (5]. "731/1270: transducers are connected to act as bothtransmitters and [58] Fieid 73/194 A 189 receivers. The time of travelof a pulse of ultrasound in the direction of flow is compared with thetime of travel of a pulse of ultrasound in the reverse direction. Thefluid paths [56} References cued traversed are thus identical, but thepulses are slightly UNITED STATES PATENTS Separated time- 2,669,1212/1954 Garman et al. ..73/l94 A 6 Claims, 3 Drawing Figures BACKGROUNDOF THE INVENTION The invention relates to apparatus for measuring theflow velocity of fluids.

Fluid flow velocity may be deduced from measurements of the time takenfor pressure waves in the fluid to traverse a predetermined pathrespectively in the direction of flow and opposite to the direction offlow. The measurements may be carried out with two pairs of transducers,each pair comprising a transmitter and a receiver of, for example,ultrasonic pressure wave pulses. The transducers are arranged so thatthe ultrasonic pulses travel in opposite directions along parallel equallength paths positioned as close together as possible.

A disadvantage of this technique is that small differences between thetwo transmission paths, such as differences in temperature of the fluid,can cause serious errors in the measurement of the fluid velocitySUMMARY OF THE INVENTION The invention provides apparatus for measuringa flow velocity or velocity component of a fluid, which apparatuscomprises first and second units arranged spaced apart to define asingle path extending through the fluid in the direction in which flowvelocity or flow velocity component is to be measured, each of whichunits comprises a single transducer capable of operating as atransmitter and as a receiver of pressure wave pulses, first pulsegenerator means operative, when triggered, to cause the first unit totransmit a pressure wave pulse, second pulse generator means operative,when triggered, to cause the second unit to transmit a pressure wavepulse, means for re-triggering the first pulse generator means uponreception of a pressure wave pulse by the second unit, means forre-triggering the second pulse generator means upon reception of apressure wave pulse by the first unit, means inhibiting there-triggering except during a predetermined period embracing theexpected reception of a pulse, means for introducing, when necessary,delay in the retriggering of the pulse generator means to avoidsimultaneous transmission and reception of a pulse by either of theunits, whereby in operation the first and second units each transmit andreceive continuously trains of pressure wave pulses travelling over thesame path in the fluid but in opposite directions without clash ateither unit between the moment of reception of an individual pulse at aunit and the moment of transmission of a pulse from that unit, and meansfor indicating the difference in frequency of pulse repetition of thefirst unit from the second.

Preferablythe transducers are ultrasonic electromechanical transducers.

Preferably a first coincidence detector is arranged to provide an outputsignal when the second unit transmits a pulse within a predeterminedshort period after the first unit transmits a pulse. Preferably controlmeans responsive to an output signal from the first coincidence detectoroperates to delay the next pulse transmission of the first unit suchthat this occurs well after the next successive pulse transmission ofthe second unit. In this way the number of output signals per unit timefrom the first coincidence detector is proportional to fluid flowvelocity when this is in the direction from the second unit towards thefirst Preferably a second coincidence detector is arranged to provide anoutput signal when the first unit transmits a pulse within apredetermined short period after the second unit transmits a pulse andpreferably further control means responsive to an output signal from thesecond coincidence detector operates to delay the next pulsetransmission of the second unit such that this occurs well after thenext successive pulse transmission of the first unit. In this way thenumber of output signals per unit time from the second coincidencedetector is proportional to fluid flow velocity when this is in thedirection from the first unit towards the second.

BRIEF DESCRIPTION OF THE DRAWINGS A specific construction of apparatusembodying the invention will now be described by way of example and withreference to the accompanying drawings in which:

FIG. 1 is a diagrammatic side sectional view of part of the apparatus,

FIG. 2 is a diagrammatic side sectional view similar to FIG. 1 butshowing more of the electronic apparatus, and

FIG. 3 is a diagrammatic representation of pulse successions forillustrating the operation of the apparatus.

DESCRIPTION OF PREFERRED EMBODIMENT In this example, the apparatus isset up for measuring the flow velocity of the liquid 11 through a pipe12.

Transducers l3 and 14 are arranged spaced apart along the length of thepipe 12. The transducer 13 forms part of a combined transmitter andreceiver 'of ultrasonic pressure wave pulses. The transducer 14 formspart of a second combined transmitter and receiver similar to the firstunit. FIG. 1 illustrates the essential components of these units. Thefirst unit has transmitter TX 1 and receiver RX 2 and the second unithas transmitter TX 2 and receiver RX 1.

Referring to FIG. 2, a start signal on line 15 triggers the transmitterTX 1 and an ultrasonic pulse is emitted from transducer 13. This pulseis received by transducer 14 detected and amplified by receiver RX 1 andapplied to a Zero crossover" timing discriminator 16. The output signalfrom the discriminator 16 is passed via an electronic switch 17 and anOR gate 18 to line 19. This line 19 is connected to transmitter TX 1 soas to re-trigger the transmitter TX 1. In this way a succession ofpulses is generated at transducer 13 and received at transducer 14 andthe pulse repetition rate is inversely proportional to the time oftravel of the pulses between the transducers l3 and 14.

A succession of pulses travelling from transducer 14 to transducer 13 issimilarly generated by transmitter TX 2 started by a signal on line 15a.The components which operate in an exactly comparable way with thosedescribed for the circuit of transmitter TX 1 are referenced with thesame reference numerals distinguished by the suffix a.

In order that the transmission pulses from transmitter TX 2 should notgenerate a re-triggering pulse for transmitter TX I and also to avoid orreduce the possibility of spurious generation of re-triggering signals,the discriminator 16 is controlled so that it is operative only for aperiod encompassing the expected time of arrival of a received pulse atthe transducer 14. This control is effected by strobe" gate 21, thesignal for which is derived via delay 22 from the re-triggering signalon line 19.

Similar provision for the discriminator 16a is made with strobe gate 21aand delay 22a.

The points A, A and B, B respectively are connected together. Acoincidence gate 23 detects when the pulse of transmitter TX 2 occurswithin a predetermined short time interval after the pulse from thetransmitter TX 1. An output from the gate 23 operates the electronicswitch 17 via OR gate 24 and introduces a delay 25 into the nextre-triggering pulse from the discriminator 16. The delay is sufficientfor the next pulse from transmitter TX 1 to be well after the next pulsefrom transmitter TX 2. This action avoids the two transmitters beingtriggered too close together in time and so causing receiver paralysisduring the time needed for reception.

The number of times per second that the coincidence gate 23 detects theclose proximity in time of pulse transmissions from the two transmittersTX I and TX 2 gives a measure of the difference in transmission timesand is directly proportional to the liquid velocity. This may beexpressed mathematically as follows:

let

v= velocity of liquid in direction of the transmission path c== velocityof sound in liquid L= distance apart of transducers fl repetition rateof transmitter TX 1 f2 repetition rate of transmitter TX 2 The term (flf2) is measured by counting the number of outputs from coincidence gate23 in a given time interval. These outputs are provided on line 26.

As the coincidence gate 23 detects when the transmissions fromtransmitter TX 2 are within a short time interval after thetransmissions from transmitter TX 1, outputs on line 26 are obtainedonly when the liquid is flowing in the direction of the arrow X.

This may be appreciated from Fig. 3 in which the axis represents timeand the vertical lines above the axis represent pulses of transmitter TX1 and the vertical lines below the axis represent pulses of transmitterTX 2. As the liquid is flowing in the direction X, the time between thepulses of transmitter TX 2 is slightly shorter than that between thepulses of transmitter TX 1. At C, the coincidence gate 23 is triggeredand the next pulse of transmitter TX 1 (shown dotted in the position inwhich it would have occurred) is delayed by D. To avoid the introductionof this delay D from upsetting the (fl-f2) reading on line 26, an equalcompensating delay is introduced into the pulse succession from thetransmitter TX 2. This is indicated at E and occurs a sufficient timelater for the pulses from the two transmitters to be well separated intime. The signal for introducing this compensating delay is applied online 27a to OR gate 24a. The source of this compensating delay signal isnot shown but may, for example, be derived from another coincidence gatewhich detects when the pulse from transmitter TX 2 occurs approximatelymidway in time between successive pulses from transmitter TX 2. The nexttriggering of gate 23 and consequent delay in the pulse transmissionsfrom transmitter TX 1 is shown in FIG. 3 at c and D.

It will be apparent from the symmetry of the arrangement that, when theliquid flow is in the direction of arrow Y, the output pulses from which(fl-f2) may be derived will be provided from coincidence gate 230 online 26a. It will be appreciated that the coincidence gate 23a detectswhen the pulse from transmitter TX 1 occurs within a given short timeinterval after the pulse from transmitter TX 2. The situation is thusthe reverse of that shown in FIG. 3. The initial delay is applied totransmitter TX 2 and the subsequent compensating delay, produced vialine 27, is applied to transmitter TX 1.

The invention is not restricted to the details of the foregoing example.For instance, in addition to measuring the flow velocity of a fluidthrough a pipeline, the apparatus may be employed for measuring anyrelative movement between a fluid and the apparatus in the line of thetwo transducers l3, 14. For example, the apparatus may be employed formeasuring the speed of a ship through water by arranging the transducers13, 14 to project into the water on a line parallel with the fore-aftaxis of the ship.

We claim:

1. Apparatus for measuring a flow velocity or velocity component of afluid, which apparatus comprises first and second units arranged spacedapart to define a single path extending through the fluid in thedirection in which flow velocity or How velocity component is to bemeasured, each of which units comprises a single transducer capable ofoperating as a transmitter and as a receiver of pressure wave pulses,first pulse generator means operative, when triggered, to cause the saidfirst unit to transmit a pressure wave pulse, second pulse generatormeans operative, when triggered, to cause the said second unit totransmit a pressure wave pulse, means for retriggering the said firstpulse generator means upon reception of a pressure wave pulse by thesecond unit, means for retriggering the said second pulse generatormeans upon reception of a pressure wave pulse by the first unit, meansinhibiting said re-triggering except during a predetermined periodembracing the expected reception of a pulse, means for introducing, whennecessary, delay in the re-triggering of the pulse generator means toavoid simultaneous transmission and reception ofa pulse by either ofsaid units, whereby In operation the first and second units eachtransmit and receive continuously trains of pressure wave pulsestravelling over the same path in the fluid but in opposite directionswithout clash at either unit between the moment of reception of anindividual pulse at a said unit and the moment of transmission of apulse from that unit, and means for indicating the difference infrequency of pulse repetition of the first unit from the second.

2. Apparatus as claimed in claim 1 wherein said transducers areultrasonic electromechanical transducers.

3. Apparatus as claimed in claim 1, wherein said delay introducing meansincludes a first coincidence detector arranged to provide an outputsignal when the second unit transmits a pulse within a predeterminedshort period after the first unit transmits a pulse.

4. Apparatus as claimed in claim 3, wherein said delay introducing meansincludes control means responsive to an output signal from the firstcoincidence detector to delay the next pulse transmission of the firstunit such that this occurs well after the next successive pulsetransmission of the second unit.

5. Apparatus as claimed in claim 4, wherein said delay introducing meansincludes a second coincidence detector arranged to provide an outputsignal when the first unit trans mits a pulse within a predeterminedshort period after the second unit transmits a pulse.

6. Apparatus as claimed in claim 5, wherein said delay introducing meansincludes further control means responsive to an output signal from thesecond coincidence detector to delay the next pulse transmission of thesecond unit such that this occurs well after the next successive pulsetransmission of the first unit.

1. Apparatus for measuring a flow velocity or velocity component of afluid, which apparatus comprises first and second units arranged spacedapart to define a single path extending through the fluid in thedirection in which flow velocity or flow velocity component is to bemeasured, each of which units comprises a single transducer capable ofoperating as a transmitter and as a receiver of pressure wave pulses,first pulse generator means operative, when triggered, to cause the saidfirst unit to transmit a pressure wave pulse, second pulse generatormeans operative, when triggered, to cause the said second unit totransmit a pressure wave pulse, means for retriggering the said firstpulse generator means upon reception of a pressure wave pulse by thesecond unit, means for retriggering the said second pulse generatormeans upon reception of a pressure wave pulse by the first unit, meansinhibiting said re-triggering except during a predetermined periodembracing the expected reception of a pulse, means for introducing, whennecessary, delay in the re-triggering of the pulse generator means toavoid simultaneous transmission and reception of a pulse by either ofsaid units, whereby in operation the first and second units eachtransmit and receive continuously trains of pressure wave pulsestravelling over the same path in the fluid but in opposite directionswithout clash at either unit between the moment of reception of anindividual pulse at a said unit and the moment of transmission of apulse from that unit, and means for indicating the difference infrequency of pulse repetition of the first unit from the second. 2.Apparatus as claimed in claim 1 wherein said transducers are ultrasonicelectromechanical transducers.
 3. Apparatus as claimed in claim 1,wherein said delay introducing means includes a first coincidencedetector arranged to provide an output signal when the second unittransmits a pulse within a predetermined short period after the firstunit transmits a pulse.
 4. Apparatus as claimed in claim 3, wherein saiddelay introducing means includes control means responsive to an outputsignal from the first coincidence detector to delay the next pulsetransmission of the first unit such that this occurs well after the nextsuccessive pulse transmission of the second unit.
 5. Apparatus asclaimed in claim 4, wherein said delay introducing means includes asecond coincidence detector arranged to provide an output signal whenthe first unit transmits a pulse within a predetermined short periodafter the second unit transmits a pulse.
 6. Apparatus as claimed inclaim 5, wherein said delay introducing means includes further controlmeans responsive to an output signal from the second coincidencedetector to delay the next pulse transmission of the second unit suchthat this occurs well after the next successive pulse transmission ofthe first unit.